Whenever sensitive electronic equipment is connected to an outdoor cable steps must be taken to insure that voltage transients caused by lightning and utility power systems do not damage the equipment. Telephone equipment and instrumentation are particularly prone to damage from voltage surges due to the large number of interconnecting and exposed telephone lines in operation. The telephone signal from a telephone handset in propagation along the connecting telephone lines becomes attenuated with distance and requires some means of electrical amplification in order to assure that the signal will reach its destination. A common method for amplifying telephone signals involves the use of a large number of telephone repeaters in a sealed exterior mounted repeater housing. A large number of incoming telephone lines can therefore be connected to the repeaters for amplification. Telephone repeater design has progressed from simple electromagnetic devices to sophisticated and miniaturized semiconductor components and circuits. The repeaters currently employed are sensitive to the current and voltage surges that frequently occur along the telephone line extent.
Along with the development of semiconductor repeaters a corresponding development has occurred in the state-of-the-art of voltage surge protective devices. Earlier protective devices connected between the telephone line and the telephone repeaters consisted primarily of carbon block devices which provided a ground path for large voltage surges and thereby prevented the voltage surges from damaging the repeaters. The problems inherent within the carbon block protector led to the development of gas-filled voltage surge protectors. In an earlier application, one of the electrodes of the gas tube was connected to one of the telephone lines before coupling with one of the repeater terminals, while the other gas tube electrode was connected to ground. In operation the telephone signals could readily transfer to the repeater since the gas tube performed like an open circuit to ground as the voltages developed in ordinary telephone communication signals were much lower than the ionization voltage required to ignite the gas tube. However, when a large voltage became impressed upon the telephone line the voltage between the tube terminal and ground, in excess of the ionization voltage for the tube, summarily caused the tube to become conductive and a short circuit discharge path was therefore established between the telephone line and ground via the electrode to ground connection through the tube. The dissipation of the abnormal voltage surge through the tube therefore protects the repeater from becoming subjected to voltages much higher than the design consideration for the repeater operation.
One of the early problems in the use of high voltage arrestors for repeater protection was the remoteness between the assembly of repeaters and the location of the protective device. In cases, for example, where the arrestor became damaged and failed to protect the corresponding electrically connected repeater, and where the repeater became damaged as a result of the aforementioned voltage surge, it was very difficult to determine which of the many voltage arrestors had failed, and which of the many separately located repeaters was associated with the defective voltage surge arrestor.
The subsequent method of arranging both the telephone repeaters and the protective high voltage surge arrestors within the same housing provided a great convenience to the telephone repairman when problems occurred. Test procedures were developed for locating and identifying both the damaged repeater and the defective arrestor so that repairs and replacement could be made within a reasonable period of time.
The methods currently employed in wiring repeater housings however require separate assemblies for the voltage surge arrestors, the repeaters, and the interconnecting wiring connection subassembly. The use of the interconnecting subassembly between the arrestors and repeaters is required since a separate arrestor is required for connecting between each input terminal of the same repeater. Since two telephone lines are required for ordinary telephone communication purposes, two two-electrode voltage arrestors must be connected in common with the input repeater terminals and two two-electrode voltage arrestors must be connected to the repeater output terminals. This is to insure that the repeater is protected at both its input and output stages since voltage surges could possibly occur on both the input terminal connecting telephone lines and the output terminal connecting telephone lines. The advent of the three-electrode gas-tube voltage surge arrestor, where a third electrode is inserted between the two primary electrodes, reduced the actual number of voltage arrestors from four per repeater to two. The center electrode, by connection to ground, provided an escape path for voltage surges which would occur on either of the two main electrodes. The use of the three-electrode voltage arrestor also greatly reduced the amount of wiring and expense required within the telephone repeater housing.
One problem involved in state-of-the-art voltage arrestor applications is the requirement for a separate wiring subassembly for connecting the telephone wires to the voltage arrestors and to the repeaters. The use of a separate voltage arrestor assembly, a separate repeater assembly, and a separate connector subassembly requires a good deal of valuable space and time for interconnecting between the voltage arrestor assembly and the connector subassembly, between the connector subassembly and the repeater input terminals, between the repeater output terminals and the connector subassembly and between the connector subassembly and the voltage arrestor assembly.
This invention therefore discloses a multi-terminal voltage surge protection device which provides for direct connection between the telephone lines and telephone repeaters and allows complete voltage surge protection without the necessity for a subassembly connector, and also provides for rapid access to the repeaters and arrestors for inspection, removal and repair.